SAN FRANCISCO (Reuters) - Google Inc. has acquired GrandCentral Communications, a start-up that lets users manage their existing phones and voice mailboxes over the Web as if they were a single account, the company said on Monday.

Financial terms were not disclosed.

Grand Central of Fremont, California is one of dozens of innovative companies that are taking advantage of Web-based software to allow consumers and businesses to make voice calls over the Internet while also working with regular phones.

GrandCentral was founded in late 2005 by Craig Walker and Vincent Paquet, who worked together while running Web-calling pioneer Dialpad Communications. Google's biggest rival, Yahoo Inc., acquired Dialpad in June 2005.

"You get a single phone number that forwards to all of your phones, giving you one number for life," Walker and Paquet said in a statement on GrandCentral's Web site confirming the deal.

EBay Inc. unit Skype, a pioneer in the Internet phone market, has signed up more than 200 million users for its free or low-cost phone services globally. Newer names in the field include venture-backed firms Jajah, Jangl, Jaxtr and Rebtel, which together have signed up millions of users in just the past year.

The idea for GrandCentral was borne out of Walker's frustration upon landing at a local airport and realizing he needed to check three voicemail mail boxes -- one for his cell phone, another for work and one for his Blackberry phone.

"If you have multiple phone numbers (e.g., home, work, cell), you get one phone number that you can set to ring all, some, or none of your phones," Wesley Chan, a Google product manager, said in a blog post on his company's Web site.

"This way, your phone number is tied to you, and not your location or job," he said.

Rather than competing directly with the likes of Vodafone Plc or China Telecom Corp. Ltd., many of these newer Web-based calling services are focused on incorporating phone-like talk features into Internet services on blogs or social network sites like MySpace or Facebook.

Konstantin Guericke, the co-founder of Silicon Valley-based business networking site LinkedIn, took over as the chief executive of Web-calling service Jaxtr late last year.

"The way I see it, social networks and blogs are about communication and the phone hasn't been really in the mix," Guericke told Reuters following news of Google's acquisition.

GrandCentral has been holding public tests of its service for several months. Current GrandCentral customers will continue to have uninterrupted service, Google said.

However, one feature that allowed users to upload their own audio tracks to create ringtones now will be limited to licensed music, GrandCentral said on its own site.

A limited number of invitations to receive GrandCentral unified numbers will be available for users who sign up at http://www.grandcentral.com, it said.

"We think GrandCentral's technology fits well into Google's efforts to provide services that enhance the collaborative exchange of information between our users," Chan said. Google did not disclose future products plans it has in the area.

But voice-calling features will quickly be built into many popular Web sites over the next three months to a year, Guericke said. "We think there is a billion-dollar business to be built, so we have no plans to get acquired any time soon."

In the last five weeks, Jaxtr has seen the number of registered users of its service on sites like Facebook grow to 300,000 users from 100,000 on May 25, he said.Capitalize on this good fortune, one word can bring you round ... changes.